Principle and Characteristics of Laser Processing

Laser processing principle:

Laser processing is based on the photothermal effect, which uses the energy of light to reach a high energy density in the focus after focusing through a lens. Laser processing does not require tools, has fast processing speed and small surface deformation, and can process various materials. Laser beams are used for various processing of materials, such as drilling, cutting, slicing, welding, heat treatment, etc. Some substances with metastable energy level will absorb light energy under the excitation of external photons, so that the number of atoms at high energy level is larger than that of atoms at low energy level, i.e. the number of particles is reversed. If there is a beam of light, the energy of photons equals the difference between the two energies, then stimulated radiation will be produced and a large amount of light energy will be output.

Characteristic

From the point of view of the application field of global laser products, the material processing industry is still the main application market, accounting for 35.2%; the communications industry ranks second, accounting for 30.6%; in addition, the data storage industry occupies the third place, accounting for 12.6%.

Compared with traditional processing technology, laser processing technology has many advantages, such as less material waste, obvious cost effect in large-scale production, and strong adaptability to processing objects. In Europe, laser technology is used to weld special materials such as high-end automobile shell and base, aircraft wing and spacecraft fuselage.

1. The laser power density is high, the temperature of the workpiece increases rapidly after absorbing the laser, and the workpiece melts or vaporizes. Even materials with high melting point, high hardness and brittleness (such as ceramics, diamond, etc.) can be processed by laser.

2. There is no contact between laser head and workpiece, and there is no tool wear problem.

3. The workpiece is free from stress and is not easily polluted.

4. It can process moving workpieces or materials sealed in glass shells.

5. The divergence angle of laser beam can be less than 1 milliarc, the diameter of laser spot can be as small as micron, and the action time can be as short as nanosecond and picosecond. At the same time, the continuous output power of high power laser can be as high as kilowatt to 10 kilowatt. Therefore, laser is suitable for both precision micro-processing and large-scale material processing.

6. The laser beam is easy to control and combine with precision machinery, precision measurement technology and computer to realize high automation and high processing accuracy.

7. In harsh environments or places where it is difficult for others to access, laser processing can be carried out by robots.

laser cutting

Laser cutting technology is widely used in the processing of metal and non-metal materials, which can greatly reduce processing time, reduce processing costs and improve the quality of the workpiece. Laser cutting is realized by using high power density energy produced by laser focusing. Compared with traditional sheet metal processing methods, laser cutting has the advantages of high cutting quality, high cutting speed, high flexibility (arbitrary shape can be cut at will), wide material adaptability and so on.

(1) Laser Melting Cutting

In laser melting cutting, the workpiece is partially melted and the melted material is sprayed out by means of air flow. Because material transfer occurs only in its liquid state, this process is called laser melting cutting.

Laser beams coupled with high purity inert cutting gas make the melted material leave the slot, while the gas itself does not participate in cutting.

—— Laser melting cutting can achieve higher cutting speed than gasification cutting. Gasification usually requires more energy than melting the material. In laser melting cutting, the laser beam is only partially absorbed.

—— The maximum cutting speed increases with the increase of laser power, and decreases almost inversely with the increase of plate thickness and melting temperature. When the laser power is constant, the limiting factor is the pressure at the slit and the thermal conductivity of the material.

—— Laser melting cutting can obtain non-oxidizing notches for iron and titanium metals.

—— The laser power density produced by melting but not gasification is between 104W/cm² ~105W/cm² for steel materials.

(2) Laser Flame Cutting

The difference between laser flame cutting and laser melting cutting is that oxygen is used as cutting gas. By means of the interaction between oxygen and the heated metal, a chemical reaction is produced to further heat the material. For structural steels with the same thickness, the cutting rate obtained by this method is higher than that by melting cutting.

On the other hand, the quality of incision may be worse than that of melt cutting. In fact, it produces wider slits, more obvious roughness, more heat-affected zones and worse edge quality.

—— Laser flame cutting is not good for processing precision models and sharp corners (there is a danger of burning the sharp corners). Pulse mode lasers can be used to limit thermal effects.

—— The cutting speed is determined by the laser power used. In the case of a certain laser power, the limiting factor is the supply of oxygen and the thermal conductivity of the material.

(3) Laser gasification cutting

In the process of laser gasification cutting, the material is gasified at the cutting seam, which requires very high laser power.

In order to prevent material vapor from condensing to the cutting wall, the thickness of the material must not exceed the diameter of the laser beam. This process is therefore only suitable for applications where the removal of molten materials must be avoided. This process is actually used only in very small areas of application of ferroalloys.

This process cannot be used, such as wood and some ceramics, where there is no melting state and therefore it is unlikely that the vapor of the material can be re-condensed.